1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, in particular, to a method of manufacturing a semiconductor device using liquid immersion lithography and a liquid immersion lithography system.
2. Description of the Related Art
As a next-generation lithography technique for 193 nm lithography, the development of 193 nm liquid immersion lithography has been advanced. A schematic diagram of a liquid immersion lithography apparatus is shown in FIG. 1.
As shown in FIG. 1, in liquid immersion lithography, a part between a last element of an objective lens of the lithography apparatus and a semiconductor substrate (wafer) on which a resist film serving as a focusing target is formed is filled with liquid (liquid immersion fluid) having a refraction index higher than that of the air. In 193 nm liquid immersion lithography, as a liquid immersion fluid, pure water having a refraction index of about 1.44 is examined. A structure (to be referred to as a shower head hereinafter) to hold the liquid immersion fluid on the wafer is fixed around a projective lens. A wafer stage for holding a wafer is driven to expose a desired position on the wafer. In operations such as exposure of a unit exposure region (to be referred to as a shot hereinafter) presented on a peripheral part of the wafer, insertion or withdrawal of a wafer, and mark detection on a wafer for an overlay mark, the liquid immersion fluid held by the shower head passes through an edge of the wafer. In an exposing operation for the shot of the peripheral part of the wafer, in order to hold the liquid immersion fluid, a table cover plate the level of which is almost adjusted to an upper surface of the wafer is arranged on the upper part of the wafer stage to wind the wafer.
An example of a relative moving path of the shower head to the wafer is shown in FIG. 2.
When the adhesiveness between the film formed on the wafer and the wafer is insufficient, the film may be peeled when the liquid immersion fluid passes through the edge of the wafer. This situation is described in Document 1. It is understood that the relative movement between the liquid immersion fluid and the wafer should cause peeling of the film at the edge of the wafer on an upper surface side of the wafer which may be in contact with the liquid immersion fluid and on a side surface of the wafer where a flow of liquid immersion fluid is supposed to be disturbed.
As described in Document 1, particles are made from the peeled film, held in the liquid immersion fluid to be present on the optical path, and may be transferred on a pattern on the wafer. Even though the peeled films are not curled like particles and kept in the shapes of flakes, the peeled films may serve as origin of a pattern defect in any case because refraction indexes of the films and the liquid immersion fluid are different from each other and because the films cannot be kept perpendicular to a plurality of refracted lights.
When moving of a wafer stage in the liquid immersion lithography apparatus is considered, particles generated at an edge of a certain wafer are conveyed to a position on the wafer different from a particle generating portion on the wafer and remains in accordance with relative movement between the liquid immersion fluid and the wafer. On the other hand, in a shot exposing operation which is later in the shot exposure order, when the liquid immersion fluid passes through a particle remaining position, the particles remaining in the liquid immersion fluid are taken in again, and a defect may be transferred to still another position.
The particles taken in the liquid immersion fluid may remain on the table cover plate of the wafer stage and on a side surface of the table cover plate which is a gap between the side surface of the table cover plate and the side surface of the wafer. In this case, as in the case where the particles remain on the wafer, the particles are taken in the liquid immersion fluid by the relative passing of the liquid immersion fluid which occurs again, and the defect is transferred to a different position on the wafer again. Alternatively, the particles remain on the wafer. The wafer influenced by the particles remaining on the table cover plate of the wafer stage may be on the same wafer as that on which film peeling occurs depending on the remaining positions of the particles and a flow of the liquid immersion fluid in the shower head, or may be on the subsequent wafer.
FIG. 3 shows a film peeling position (black star sign) which is a particle generating source, a defect position (X sign) to which a particle is transferred, a position (white start sign) where a particle remains on a wafer, a defect (white triangular sign) transferred when the particle is taken in the liquid immersion fluid again, a position (black lozenged sign) where a particle remains on the wafer stage, and a position (plus sign) of a defect transferred when the particle remaining on the wafer stage is taken in the wafer again.
Document 2 describes some particle formation mechanism and tool cleaning concern. However, Document 2 does not describe timing at which tool cleaning is performed and a trigger for the cleaning at all.
In Document 3, research members including the present inventor have reported that liquid immersion fluid remaining on a wafer forms a watermark as a pattern defect.
Document 1: Lin john C. H., “193-nm immersion lithography for 65-nm node and below” (oral presentation), p. 24, 2nd International Symposium on Immersion Lithography, 12-15 Sep. 2005
Document 2: Ching-Yu Chang et al., “Advanced Lithography Material Needs for Immersion and Beyond” THE 26th TOKYO OHKA SEMINAR, Dec. 6, 2005
Document 3: D. Kawamura, et al., “Influence of the Watermark in Immersion Lithography Process”, Proc. SPIE vol. 5753, pp. 818-826 (2005).